linux-kernel - [PATCH 4.1 248/267] nfs: fix potential credential leak in ff_layout_update_mirror

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Date:	Fri, 31 Jul 2015 12:41:39 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jeff Layton <jeff.layton@...marydata.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>
Subject: [PATCH 4.1 248/267] nfs: fix potential credential leak in ff_layout_update_mirror_cred

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Layton <jlayton@...chiereds.net>

commit a24221dca1868101c9b4b5adde4a6a5b1a3a64a7 upstream.

If we have two tasks racing to update a mirror's credentials, then they
can end up leaking one (or more) sets of credentials. The first task
will set mirror->cred and then the second task will just overwrite it.

Use a cmpxchg to ensure that the creds are only set once. If we get to
the point where we would set mirror->cred and find that they're already
set, then we just release the creds that were just found.

Signed-off-by: Jeff Layton <jeff.layton@...marydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@...marydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfs/flexfilelayout/flexfilelayoutdev.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/nfs/flexfilelayout/flexfilelayoutdev.c
+++ b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
@@ -324,7 +324,8 @@ static int ff_layout_update_mirror_cred(
 				__func__, PTR_ERR(cred));
 			return PTR_ERR(cred);
 		} else {
-			mirror->cred = cred;
+			if (cmpxchg(&mirror->cred, NULL, cred))
+				put_rpccred(cred);
 		}
 	}
 	return 0;


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